This invention relates generally to the field of telecommunications networks, and more particularly to a method and system for allocating bandwidth and buffer resources to constant bit rate (CBR) traffic in a telecommunications network.
Telecommunications networks have traditionally been circuit-switch networks that have transmission paths dedicated to specific users for the duration of a call and that employ continuous, fixed-bandwidth transmission. Due to growth in data traffic created by the Internet and its related technologies, however, telecommunications networks are being moved to a packet-switching transmission model. Packet-switch networks provide a large range of digital services, from data to video to basic voice telephony. Packet-switch networks can allow dynamic bandwidth and may be connectionless with no dedicated path or connection-oriented with virtual circuits and dedicated bandwidth along a predetermined path.
Asynchronous transfer mode (ATM) is a connection-oriented packet-switching technology in which information is organized into small, fixed length cells. ATM carries data asynchronously, automatically assigning data cells to available time slots on demand to provide maximum throughput. Compared with other network technologies, ATM provides large increases in maximum supported bandwidth, designed-in asynchronous traffic support, support for multiple types of traffic such as data, video, and voice transmissions on shared communication lines, and virtual networking capabilities, which increase bandwidth utilization with high quality of service and ease network administration.
ATM cells are routed through a telecommunications network at high speeds using a switching label included in the cell. The switching label has two sections that define a virtual path (VP) and a virtual channel (VC) in the network through which the cell is routed. The use of virtual paths and virtual channels allows physical bandwidth in the network to be subdivided and separately commercialized.
Because of the low latency and predictability throughput ATM offers, it is capable of providing quality of service (QoS) features. QoS is defined in terms of the attributes of end-to-end ATM connections and is important in an integrated service network, particularly for delay-sensitive and/or loss sensitive applications such as audio and video transmissions, as well as voice-over IP. Other applications in which QoS may be important include traditional data communications, imaging, full-motion video, and multimedia, as well as voice.
Performance criteria for describing QoS for a particular connection include cell loss rate (CLR), cell transfer delay (CTD), and cell delay variation (CDV). ATM traffic is classified as either constant bit rate (CBR) traffic, real-time variable bit rate (rt-VBR) traffic, non real-time variable bit rate (nrt-VBR) traffic, available bit rate (ABR) traffic, and unspecified bit rate (UBR) traffic depending on the QoS parameters applied to the traffic. CBR and rt-VBR traffic visualize dedicated bandwidth and are intended for real time applications. ABR and nrt-VBR traffic is intended for non-real time applications which can control, on demand, their transmission rate in a certain range. Like ASR, UBR traffic is intended for non-real time applications which do not have any constraints on the cell delay and cell delay variations.
CBR traffic parameters include peak cell rate (PCR) and cell delay variation tolerance (CDVT) performance criteria which allows little or no cell loss, low cell delay, and low cell delay variation. Accordingly, traffic in a CBR connection arrives almost periodically with variations from the periodic rate at previous transmission stages causing cell clumping. To prevent cell loss in clumping conditions, additional bandwidth and buffer resources may need to be allocated.
Previous methods for allocating bandwidth and buffers to CBR connections have used various approximate queuing models, such as D/D/1 and N/D/1 which are not accurate and cannot insure QoS guaranties for some scenarios.
The present invention provides an improved method and system for allocating bandwidth and buffer resources to constant rate traffic that substantially eliminates or reduces disadvantages and problems associated with previous systems and methods. In particular, minimum bandwidth and buffer resources that are necessary to ensure constant rate connections achieve zero cell loss and guaranteed cell delay are allocated at a port or link.
In accordance with one embodiment of the present invention, a method for allocating transmission resources to a constant rate connection includes determining a maximum cell clumping value for a constant rate connection based on a peak cell rate and a cell delay variation tolerance for the constant rate connection. An allocation bandwidth is determined for the constant rate connection based on the maximum cell clumping value. The allocation bandwidth comprises the bandwidth at which no cells of the constant rate connection are lost and the cell delay variation tolerance for the constant rate connection is satisfied. The allocation bandwidth is allocated at a network element for transmission of the constant rate connection.
More particularly, in accordance with another aspect of the present invention, an allocation buffer size for the constant rate connection is determined based on the maximum cell clumping value in the allocation bandwidth. The allocation buffer size comprises a buffer size at which no cells are lost for the constant rate connection and the cell delay variation tolerance is satisfied. The allocation buffer size is allocated at the network element for transmission of the constant rate connection. The constant rate connection may comprise a constant bit rate (CBR) asynchronous transfer mode (ATM) or other suitable connection.
Technical advantages of the present invention include providing an improved method and system for allocation bandwidth and other suitable resources to CBR and other suitable traffic in a telecommunications network. In particular, bandwidth and buffer resources are allocated to a connection based on standardized traffic parameters for that connection. As a result, the allocated bandwidth and buffer size are accurate for all scenarios and parameter ranges. Service requirements are therefore completely guaranteed. In addition, the allocation methodology conforms to standardize traffic descriptors and can be efficiently implemented for real-time application in a network element.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.